1. Field of the Invention
The present invention relates to a solenoid of simplified construction.
2. Description of the Prior Art
In certain applications, such as microwave coaxial switches, it is necessary to provide multiple, small solenoids for moving mechanical components in response to electrical control signals. For example, a typical microwave switch may have a single coaxial input port and three, four, five or more output ports. A mechanical arrangement of movable leaf contacts is used to connect the input port alternatively to a selected one of the output ports.
In such a switch, to maintain the necessary impedance, insertion loss, isolation and VSWR characteristics, the movable leaf contacts must be situated in small, closely adjacent but isolated channels. Imparting the necessary mechanical movement to these leaf switches necessiates the use of multiple solenoids which are compact enough in size to fit closely within the small switch package, that typically has an overall height in the order of two to three inches, and an overall diameter of three inches or less.
Perhaps more important than small size, in such applications, is the necessity that each solenoid have positive, failure free operation through hundreds of thousands of operating cycles. Should one of the solenoids not function even intermittently, the entire switch assembly would have to be removed and disassembled for repair, an operation that is costly both in terms of repair time itself and in down time of the equipment in which the switch is located.
Thus there is a need for a positive acting solenoid, small in size, which by its construction has minimal likelihood of failure, and it is an objective of the present invention to provide such a solenoid.
One common failure mechanism of prior art solenoids resulted from the use of epoxy or other adhesives to hold the coil bobbin within the solenoid structure. Often residual films of the epoxy or other adhesive would accumulate on the armature bearing surface. Such buildup would lead to occasional binding of the armature, thereby preventing or impeding its normal movement. This resulted in intermittent operation of the associated microwave switch, since occasionally armature movement would be insufficient to move the switch leaf contact all the way between the "break" and "make" positions.
Thus another object of the present invention is to provide a solenoid which uses no adhesives in its assembly.
Another failure mode of prior art solenoids was wear or erosion of the bushings for the armature or solenoid shaft or plunger. Such mechanical wear could result in improper seating of the armature or plunger. As a result, the movement may deviate from the desired direction or distance, again causing intermittent operation of the microwave switch in which the solenoid is employed.
It is another object of the present invention to provide a solenoid in which there is very little wear and tear, and in which even if some wear of the bushing components should occur, positive operation of the solenoid would not be impaired.